1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus, or similar image forming apparatus, and more specifically to an image forming apparatus with an improved cleaning operation and mechanism.
2. Description of the Background Art
An image forming apparatus of the type using an electrostatic image transfer system is known and is configured to form an electric field between a photoconductive drum or similar image carrier and an intermediate image transfer body, sheet conveyor, or similar moving member for thereby transferring a toner image formed on the image carrier. In that type of image forming apparatus, some residual toner is left on the image carrier after the transfer of the toner image to a subject body, e.g., after transfer to the intermediate image transfer body or to a sheet or recording member. If part of the image carrier on which such residual toner is present is subject to the next image formation, then irregular charging or similar defective charging can occur on the noted part of the image carrier, which lowers image quality. It is a common practice to remove the residual toner from the image carrier with a cleaning device. The problem with such a cleaning device is that it needs an extra space for accommodating a waste toner tank configured to store the residual toner collected from the image carrier and a recycling path along which the residual toner is conveyed to be reused, making the entire apparatus bulky. Particularly, a current trend in the imaging art is toward a tandem image forming apparatus that assigns a particular image carrier to each color to meet the increasing demand for high-speed color image formation. If a cleaning device is utilized in this kind of image forming apparatus, then a particular cleaning device must be assigned to each of a plurality of image carriers, making the above problem more serious.
To solve the problem stated above, Japanese Patent No. 3,091,323 discloses an image forming apparatus using a simultaneous developing and cleaning system that causes a developing device to also collect residual toner. More specifically, the developing device, first used to develop a latent image, is also used as a cleaning device at the same time, so that a particular cleaning device does not have to be assigned to each image carrier. This contributes a great deal to the size reduction of the apparatus.
Also, the image forming apparatus disclosed in Japanese Laid-open publication No. 2000-181200 includes a toner removing structure to remove toner from charging device after the charging device charges an image carrier. The charging device deposits polarity control grains, by which the polarity of toner grains is changed to a same polarity as the image carrier. According to this publication, residual toner having an opposite polarity is electrically deposited on the charging device. Then, the polarity of the residual toner having opposite polarity is changed to the regular polarity by contacting with the charging device. Changing a polarity of the residual toner is effectively performed at a contact portion between the charging device and the toner removing structure. The residual toner changed to the regular polarity is then removed at the contact portion, so that the residual toner is returned to the image carrier. Meanwhile, the residual toner not removed is conveyed to a charging area of the charging device, and then is electrically discharged to the image carrier, by using the difference of electrical potential between the charging device and the image carrier.
Further, the image forming apparatus disclosed in Japanese Laid-open publication No. 2001-215799 includes a toner electrical potential controlling device, which slides in a direction of an image carrier axis, mounted on an upper area from a charging device in a direction of movement of the image carrier.
Also, in the image forming apparatus disclosed in Japanese Laid-open publication No. 10-213945, a different linear velocity is utilized between an image carrier and a charging device.